This invention relates to a flow control unit for use in a gun system for injecting foam insulation into a wall cavity and, in particular, to detecting means for automatically inhibiting the flow control unit in the event the injection gun is turned off.
In U.S. Pat. No. 4,204,612, there is disclosed a control system for accurately regulating the amount of resin and foaming agent delivered to the mixing chamber of an injecting gun. As noted in this patent, it is extremely important for the production of quality foam insulation having a high R value that the two components be mixed in the proper amounts at the point of injection. Any slight deviation from the optimum flow rate will cause the insulation to fail. To overcome this difficulty, flow detecting means are positioned in the lines bringing resin and foaming agent to the gun and providing an output signal indicative of the flow rate in each line. The flow rate is compared to preselected upper and lower limits and, if the actual flow is outside of the selected limits, a control valve in the line is automatically adjusted to bring the flow back into limits.
Initially, a switch was positioned upon the gun which, when manually closed, informed the flow control circuitry that the operator had shut the gun down. However, prior to closing the switch the control circuitry, not knowing that the gun had been turned off, would initiate corrective action that invariably would tend to move the control valves into a wide open position. Turning the gun on again would cause the control system to compensate in the other direction in an attempt to bring the flow back into limits. Because of the initial open position of the valves, it generally took some time for the system to "settle down". During this time less than quality foam was being produced. Besides being wasteful, the manually operated switch arrangement produced a good deal of wear on the mechanical components of the system and introduced operational problems in regard to the electrical control circuitry.